Ti doping as an effective strategy for increasing the stability of strontium-copper-iron perovskite-based oxygen carriers
Rafal Lysowski, Ewelina Ksepko
Abstract
Strontium ferrite perovskites are a class of nonstoichiometric materials known for their oxygen-transport properties. Oxygen-deficient perovskites can be applied as oxygen-transport membranes or oxygen carriers (OCs) in the chemical looping combustion (CLC) process, which is a promising technology for flameless fuel combustion. As the cost of an OC is a critical factor in the overall cost-effectiveness of the CLC process, the OC developed for CLC must exhibit good oxygen-transfer capacity and physicochemical stability. However, some OCs tend to decompose under specific conditions, which can result in their deactivation or a change in their chemical properties, including their oxygen-transfer capacity. This can be overcome by heteroatom doping. This article presents the synthesis of strontium ferrite perovskites with two dopants (Cu and Ti) and demonstrates their potential as chemically stable OCs for chemical looping combustion (CLC). The ability of Cu,Ti-codoped strontium ferrite perovskites (Sr(Cu x Fe 1−x−y Ti y )O 3−δ ) to release gaseous oxygen under anaerobic conditions (via the so-called chemical looping with oxygen uncoupling (CLOU) effect) and their stability in a reducing environment evaluated in the 800–1000 °C range, using a 3 % H 2 /Ar mixture as the reducing agent and fuel in the simulated CLC process, are discussed. The best-performing perovskite-based OCs exhibit oxygen-transport capacities of 1.3 and 6 wt% in the CLOU and CLC processes, respectively. The examined materials are the first in this composition to be synthesized and proposed as solid oxygen carriers. The tested samples do not undergo phase segregation after numerous redox cycles at 800–1000 °C, unless previously reported in the literature for similar undoped compositions. Additionally, beneficially, the tested samples maintain their high reactivity toward gaseous fuel. Thus, the positive influence of Ti on the chemical stability of the OC is demonstrated.